Compositions comprising carbon nanotubes and articles formed therefrom

ABSTRACT

Improved compositions comprise a polymer and carbon fibers, such as nanotubes. In some embodiments, the carbon fibers, e.g., nanotubes, can be mechanically blended or incorporated into the polymer, while in some embodiments carbon nanotubes also may be covalently bonded to the polymer to form corresponding covalent materials. In particular, the polymer can be covalently bonded to the side walls of the carbon nanotubes to form a composite with particularly desirable mechanical properties. Specifically, the bonding of the polymer to the nanotube sidewall can provide desirable mechanical properties of the composite due to the orientation relative to other types of association between the nanotubes and the polymer. The processing of the nanotubes can be facilitated by the dispersion of the nanotubes in an aqueous solution comprising a hydrophylic polymer, such as ethyl vinyl acetate. A dispersion of nanotubes can be combined with a polymer in an extrusion process to blend the materials under high shear, such as in an extruder. In general, various articles can be formed that take advantage of the properties of the composite materials incorporating a polymer and carbon fibers, such as carbon nanotubes.

FIELD OF THE INVENTION

The invention generally relates to compositions comprising polymers andcarbon nanotubes or other carbon fibers. In particular, in someembodiments the invention relates to compositions having functionalizedcarbon nanotubes, which can be covalently attached to polymers.Additionally, the invention also relates to methods of making thecompositions. Furthermore, the invention relates to articles, such ascontainers or functional articles, that are formed from thecompositions.

BACKGROUND OF THE INVENTION

Technological developments impose increasing demands on materialproperties to achieve desired objectives. On the other hand, improvedmaterial capabilities correspondingly can provide improved performancecapabilities for corresponding products that incorporate the improvedmaterials. Furthermore, composite materials have been found to be a wayto combine desired properties of different compositions to obtain amaterial that benefits from the properties of the plurality ofcompositions.

Carbon fibers generally have been formed with a range of properties andmorphologies. In particular, carbon nanotubes, which are generallycylindrical forms of graphitic carbon, exhibit useful mechanical andelectrical properties including, for exampe, large tensile strength andlarge electrical conductivity. Carbon nanotubes can exist in single walland multiple wall forms, both of which can be prepared by chemical vapordeposition (CVD) techniques. In general, process conditions such as, forexample, deposition temperature and catalyst selection can influence theformation of the different structures. Additionally, carbon nanotubescan be electrically conducting or semiconducting, depending onstructure.

Advanced products may require special handling approaches due to thesensitivity of the products to damage and degradation. In particular,some products, such as semi-conductor devices, silicon wafers and thelike, can be damaged during transportation, and/or processing, forexample, as a result of the products contacting each other.Consequently, specialized containers have been developed to transportthese products. These specialized containers can be formed, for example,from molded thermoplastic materials, which have structure suitable forholding a plurality of products in a desired orientation within thecontainer. The interior structure of these containers typically preventsthe products from contacting each other, and thus helps reduce productdamage that can occur during transportation of the products.

Some articles have high electrical conductivities to appropriatelyfunction in their applications. Specifically, a range of componentsdelivers high electrical conductivity within a corresponding device. Forexample, many electrical generation units incorporate electricallyconductive elements. In particular, fuel cells can have bipolar platesthat provide electrical conduction between neighboring cells connectedin series while simultaneously providing for flow of fuels and oxidizingagents and preventing material flow between the neighboring cells.Similarly, many battery structures incorporate electrically conductiveelements to facilitate electrical connection of the battery poles withthe battery electrodes.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a composition comprising apolymer covalently bonded to the side walls of carbon nanotubes.Additionally, the invention pertains to an article such as, for example,electrodes, containers and the like, comprising a polymer covalentlybonded to the side walls of carbon nanotubes.

In a second aspect, the invention pertains to an aqueous dispersion ofcomprising ethyl vinyl acetate and carbon fibers. In these embodiments,the aqueous dispersion of the carbon fibers in the ethyl vinyl acetatecan facilitate injection of the nanotubes into process equipment suchas, for example, extruders.

In another aspect, the invention pertains to an article comprising apolymer and fluorinated carbon nanotubes, wherein the fluorinated carbonnanotubes provide increased resistance to chemical degradation.

In a further aspect, the invention pertains to a method of forming acomposite comprising injecting a liquid dispersion of carbon fiberswithin an extruder having a polymer within the extruder and applyingshear to the blend of carbon fibers and polymer.

In addition, the invention pertains to a wafer carrier comprising slotsfor the support of a wafer, wherein the slots comprise wafer contactpoints having a surface with a composite of polymer covalently bonded tothe carbon nanotubes.

Furthermore, the invention pertains to a fuel cell comprising a bipolarplate comprising a composite of polymer covalently bonded to carbonnanotubes.

DEATILED DESCRIPTION OF THE INVENTION

Improved compositions comprise a polymer and carbon fibers, such asnanotubes. In some embodiments, the carbon fibers, e.g., nanotubes, canbe mechanically blended or incorporated into the polymer, while in someembodiments carbon nanotubes also may be covalently bonded to thepolymer to form corresponding covalent materials. In particular, thepolymer can be covalently bonded to the side walls of the carbonnanotubes to form a composite with particularly desirable mechanicalproperties. Specifically, the bonding of the polymer to the nanotubesidewall can provide desirable mechanical properties of the compositedue to the orientation relative to other types of association betweenthe nanotubes and the polymer. The processing of the nanotubes can befacilitated by the dispersion of the nanotubes in an aqueous solutioncomprising a hydrophylic polymer, such as ethyl vinyl acetate. Adispersion of nanotubes can be combined with a polymer in an extrusionprocess to blend the materials under high shear, such as in an extruder.In general, various articles can be formed that take advantage of theproperties of the composite materials incorporating a polymer and carbonfibers, such as carbon nanotubes. Also, fluorinated nanotubes can beused to further improved the properties of the composites for certainapplications. For example, fluorination of the nanotubes can impartgreater chemical inertness, transparency and water resistance.

Due to the presence of the carbon nanotubes or carbon fibers generally,the compositions can exhibit improved physical properties such as,electrical conductivity, enhanced tensile strength, thermal stability,resistance to chemical degradation, transparency and combinationsthereof. The carbon nanotubes can be dispersed through the material,formed as a coating or incorporated into more elaborate structures. Insome embodiments, the compositions can be used to form, for example, acontainer suitable for preventing electrostatic charge build up, whichreduces the occurrence of electrostatic discharge (ESD) involving theproducts contained within the container. In other embodiments, thecompositions can be used to form electrically conductive polymerstructures such as biopolar plates, current collectors, battery pins,electrodes, gas diffusion electrodes and the like.

Carbon nanotubes are generally cylindrical forms of graphitic carbonthat exhibit useful mechanical and electrical properties. In general,carbon nanotubes can exist as single wall and multiple wall structures.Single wall carbon nanotubes are tubular structures comprising a singlegraphene sheet, while multiple wall carbon nanotubes comprise multipleconcentric graphene sheets. Single and multiple wall carbon nanotubescan be made, for example, by known catalytic chemical vapor deposition(CVD) techniques. For example, the synthesis of single wall carbonnanotubes by CVD is generally described in “Synthesis, Integration, andElectrical Properties of Individual Single-Walled Carbon Nanotubes,”Kong et al., Applied Physics A, Volume 69, pp. 305-308 (1999), which ishereby incorporated by reference herein. Synthesis of multiple wallcarbon nanotubes is generally described in “Rapid Synthesis of CarbonNanotubes by Solid-State Metathesis Reactions,” O'Loughlin et al., J.Phys. Chem. B, Volume 105, pp. 1921-1924 (2001), which is herebyincorporated by reference herein. Both forms of nanotubes arecommercially available. For example, single wall nanotubes are availablefrom CarboLex (Lexington, Ky.) and Carbon Nanotechnologies, Inc(Houston, Tex.), and multiple wall carbon nanotubes are available fromApplied Sciences Inc. (Cedarville, Ohio). With respect to the materialsdescribed herein, in some embodiments, the nanotubes can be single wallcarbon nanotubes, multiple wall carbon nanotubes or combinationsthereof. The nanotubes can be agglomerated, for example into nanotubeparticles or nanotube wires, or they can be dispersed nanotubes or acombination thereof.

Additionally, carbon nanotubes can be functionalized to impart desiredproperties to the carbon nanotubes. For example, some functionalizednanotubes can be more easily dispersed into aqueous or nonaqueousdispersions, and some functionalized nanotubes can be covalently bondedto polymers. Furthermore, functionalized nanotubes can facilitatebonding with the polymer. Fluorine functionalized nanotubes can beincorporated into composites that can have increased resistance tochemical degradation and/or increased transparency.

Some functionalization of carbon nanotubes is thought to generallyfunctionalize the nanotubes at their ends. In addition, carbon nanotubescan be functionalized along their side walls. Thus, thesefunctionalizations provide for covalent bonding of the carbon nanotubeseither at their ends and/or along the side walls. As described above,carbon nanotubes exhibit useful mechanical and electrical propertiesincluding electrical conductivity and tensile strength. For example,carbon nanotubes can conduct electricity better than copper or gold, andcan have a tensile strength that is greater than the tensile strength ofsteel. It is believed that the increased tensile strength is a result ofthe three-dimensional carbon network that forms the structure of thenanotubes.

The composites of the present disclosure can comprise carbon fibersassociated with a polymer, which can be formed into articles havingimproved properties. The improved properties of the articles can beattributed to both the properties of the nanotubes and the properties ofthe polymers. Generally, selection of a particular polymer orcombinations of polymers can be made based on the desired properties ofthe final product. For example, the selection of a polymer can be basedon desired structural properties such as, for example, tensile strength,elasticity, transparency, and the like. Suitable polymers for particulararticles are described further below. As used herein, polymer refers tolinear, branched and crosslinked covalent structures. While nanotubesare technically polymers, as used herein polymers do not includecompounds with a rigid and unique tertiary structure, such as carbonnanotubes.

As discussed above, semi-conductor devices, as well as other products,may be susceptible to damage from electrostatic discharge (ESD). Intheory, electrostatic potentials can exist whenever suitable electricalinsulators or semi-conductors are present. Specifically, materials suchas, for example, nylon, polyester, polyurethane, polyvinyl chloride andpoly(tetrafluoroethylene), tend to build up static charges. The build upof electrostatic charges in containers made from these materials canresult in electrical discharge to products, such as semi-conductordevices, located within the containers. While the amount of energytransferred through ESD is relatively small, significant damage canresult to the products located in the containers. Furthermore,conventional conductive coatings, which can be applied to containers toreduce the occurrence of ESD, tend to be degraded by recyclingprocesses, and therefore the recycled or refurbished containers have tobe re-coated with the conductive coating or replaced. As describedherein, one way of reducing ESD in containers and other products is toform the containers form an electrically conducting compositecomposition comprising a polymer associated with carbon nanotubes.

Polymer—Carbon Fiber Compositions

As described above carbon fibers can be incorporated into, for example,polymer composites to provide desired mechanical and electricalproperties by covalently bonding the carbon fibers to the polymer and/orby dispersing the fibers in a polymer. In some embodiments, the carbonfibers can be nanotubes, such as single wall carbon nanotubes multiplewall carbon nanotubes, or combinations thereof. Carbon nanotubes, whichare generally cylindrical forms of carbon, can be covalently bonded topolymer systems by functionalizing the ends and/or the side walls of thecarbon nanotubes, and subsequently reacting the functionalized nanotubewith an appropriate polymer. Additionally or alternatively, the carbonnanotubes can be incorporated into a polymer system by dispersing thecarbon nanotubes in a suitable polymer. In some embodiments, the carbonnanotubes can also be functionalized to facilitate dispersion in desiredpolymer systems. Dispersing and/or covalently bonding the carbonnanotubes into polymer systems can provide good incorporation anduniformity of the nanotubes throughout the polymer, which can enhancethe mechanical and/or electrical properties of the polymer.

Carbon fibers are chemically resistant, rigid structures that can beused to produce articles such as, for example, tennis rackets, bicyclesand golf clubs. For industrial uses, the carbon fibers can be formedinto structures, such as sheets or other shapes. Carbon fibers can beproduced from organic polymers such as, for example, poly(acrylonitrile)that are stretched and oxidized to produce precursor fibers. Theprecursor fibers can then be heated in a nitrogen environment, whichfacilitates the release of volatile compounds and yields fibers that areprimarily composed of carbon. Carbon fibers are commercially availablein varying grades, which can have varying tensile strengths and weights.As used herein, carbon fibers can be a range of carbon fiber materialsincluding, for example, carbon nanotubes. Carbon nanotubes are rolled upgraphene sheets of carbon which exhibit useful mechanical and electricalproperties. Generally, carbon nanotubes are described as comprisingtubular graphene walls which are parallel to the filament axis.Additionally, carbon nanotubes can be hollow and can have ends capswhich seal the tubular structure.

In some embodiments, the ends of single and multiple wall carbonnanotubes can be functionalized by treating the nanotubes with nitricacid (HNO₃) or a sulfuric acid (H₂SO₄)-nitric acid mixture, both ofwhich are known to remove the end caps of the carbon nanotubes andintroduce oxygen-containing functional groups such as carboxyl groups.The carboxyl groups can be further reacted to form other functionalgroups, which can then be used to covalently bind the carbon nanotubesto polymers or other compounds. For example, primary amines (RNH₂) canbe reacted with carboxyl groups to form amide linkages using carbodimidechemistry, which can result CO—NH—R groups located on the ends of thenanotubes. Furthermore, nanotubes containing carboxyl groups can berefluxed in SOCL₂, which can covert the carboxyl groups into acylchlorides that can be further reacted into polymer systems having, forexample, amine or alcohol functional groups. Generally, thefunctionalization reactions can be conducted in a suitable solvent suchas, for example, 1,2-dichlorobenzene.

Purification and end functionalization of carbon nanotubes are generallydiscussed in, for example, “Covalently Functionalized Nanotubes asNanometer-Sized Probes in Chemistry and Biology,” Wong et al., Nature,Volume 392, July, (1998), “Large-Scale Purification of Single-WallCarbon Nanotubes: Process, Product, and Characterization,” Rinzler etal., Applied Physics A, Volume 67, pp. 29-37 (1998), “StrongLuminescence of Solubilized Carbon Nanotubes,” Riggs et al., J. Am.Chem. Soc., 122, 5879-5880 (2000), and “Oxygen-Containing FunctionalGroups on Single-Wall Carbon Nanotubes: NEXAFS and VibrationalSpectroscopic Studies,” Kuznetsova et al., J. AM. Chem. Soc., Volume123, pp. 10699-10704 (2001), all of which are hereby incorporated byreference herein.

Additionally, the carbon nanotubes can be functionalized along theirsides walls, which can facilitate reacting the carbon nanotubes intodesired polymer systems. Alternatively, the carbon nanotubes may befunctionalized on both the ends and the side walls of the nanotubes. Insome embodiments, the carbon nanotubes can be reacted with fluorine gasto fluorinate the side walls of the nanotubes. The fluorinated nanotubescan be further functionalized by reactions with nucleophiles such asamines, hydrazines and alkyl lithium compounds. These side wallderivatized carbon nanotubes are described further, for example, inPublished U.S. patent application 2001/0031900A to Margrave et al.,entitled “Chemical Derivatization Of Single-Wall Carbon Nanotubes ToFacilitate Solvation Thereof: And Use Of Derivatized Nanotubes To FormCatalyzt-Containing Seed Materials For Use In Making Carbon Fibers,”incorporated herein by reference. As described above, fluorinated carbonnanotubes can be incorporated into composites to provide increasedresistance to chemical degradation and/or increased transparency.

The carbon nanotubes can also be incorporated into dispersions tofacilitate processing of the nanotubes into desired articles and/orcoating of the nanotubes onto articles. In some embodiments, thedispersion can comprise an aqueous dispersion of carbon nanotubes inethyl vinyl acetate. Ethyl vinyl acetate is sold commercially under thetrade name Bynel® by Dupont (Wilmington, Del.), under the trade namePlexar® by Equistar (Houston, Tex.), and under the trade name Evatane®by Atofina Chemicals (Philadelphia, Pa.). Generally, EVA is commerciallyavailable in various grades which can have varying vinyl acetate (VA)content (i.e., vinyl acetate monomer units in the polymer), density andmeld indices. Suitable EVA formulations for use in the presentdisclosure include, for example, EVA formulations having a VA contentfrom about 10 mole % to about 50 mole %, in further embodiments fromabout 15 mole percent to about 40 mole percent and in other embodimentsfrom about 20 mole percent to about 35 mole percent. Additionally,suitable EVA formulations can have melt indices ranging from about 2.5g/10 mn to about 800 g/10 mn at 190° C., using a 2.16 Kg load. The meltindex is evaluated using the ASTM D1238 procedure, which is herbyincorporated by reference herein. In some embodiments, the EVA can havea density ranging form about 0.92 g/cm³ to about 0.95 g/cm³. A person ofordinary skill in the art will recognize that additional ranges andsubranges of VA content, melt indices and density within the explicitranges are contemplated and are within the present disclosure. Thestructure of EVA is shown below wherein the relative amounts of the twomonomer units is represented by the n and m subscripts:

Below are tables displaying data for several grades of commerciallyavailable EVA formulations. TABLE 1 EVATANE ® VA content Melt indexMelting point Grades (%) (g/10 mn) (° C.) 24-03 23-25 2.5-3.5 79 28-0326-28   3-4.5 75 28-05 27-29 5-8 73 28-25 27-29 22-29 72

TABLE 2 ASTM Bynel^((R)) Grades Property Test Method Unit 1123 11241E554 11E573 Melt Index D1238, 190/2.16 dg/min 6.4 25 8.0 6.9 DensityD1505 g/cm³ 0.946 0.947 0.93 0.923 Melt Point DSC, D3418 ° C. (° F.) 74(165) 70 (158) 94 (201) 95 (203) Freeze Point DSC, D3418 ° C. (° F.) 51(124) 51 (124) 76 (169) 80 (176) Vicat Softening Point D1525 ° C. (° F.)50 (122) 49 (120) 68 (154) 71 (160)

In other embodiments, the carbon nanotubes can be dispersed inpoly(vinyl alcohol) (PVA). PVA is commercially sold under the trade nameElvanol® by Dupont (Wilmington, Del.), under the trade name Celvol™ byCelanese Chemicals (Dallas, Tex.), and from Erkol (Spain). Generally,suitable PVA formulations can have a molecule weight average from about10,000 to about 190,000. Below is a table which displays data forsuitable formulations of PVA. The PVA generally can have a density fromabout 1.27 to about 1.31 g/cm³. The melting point of the PVA generallycan range from about 85 to about 200° C. A person of ordinary skill inthe art will recognize that additional ranges within the explicit rangesof molecular weight, density and melting point are contemplated and arewithin the present disclosure.

The PVA can be partially or fully hydrolized. The structure of PVA isshown below wherein the relative amounts of the two monomer units isrepresented by the n subscript:

In general, PVA is formed commercially by the hydrolysis/saponificationof poly vinyl acetate or other poly vinyl small aliphatic ester. Thedegree of hydrolysis determines relative amounts of vinyl alcoholmonomer units in the polymer. TABLE 3 Grade Percent Solution Volatiles,Ash, Designations Viscosity^(a) Hydrolysis^(b) pH % max. % max.^(c)Elvanol ® 5-6 87-89 5.0-7.0 5 0.7 51-05 Elvanol ® 21-26 87-89 5.0-7.0 50.7 52-22 Elvanol ® 44-50 87-89 5.0-7.0 5 0.7 50-42^(a)Viscosity in mPa · s (cP) of a 4% solids aqueous solution at 20° C.(68° F.), determined by Hoeppler falling ball method^(b)Mole percent hydrolysis of acetate groups, dry basis^(c)Dry basis: calculated as % Na₂O

For blends of nanotubes with polymers, the presence of EVA or PVA canstabilize the adhesion or dispersion of the blend, especially foradditional structural polymers such as polyolefins, polycarbonates,polystyrene, and acrylonitrile butadiene styrene copolymers. Similarly,other polyalcohols can be used. For example, soluble starches or otherpolysaccharides and derivatives thereof can be used. Also, othercopolymers with varying degrees of vinyl monomers, vinylalcoholmonomers, and/or vinyl ester monomers can be used if sufficientlysoluble in aqueous solutions.

In other embodiments, the carbon nanotubes can be functionalized toincrease the solubility of the nanotubes in desired polymers and/orsolvents, which facilitates the formation of polymer/nanotube and/orsolvent/nanotube dispersions. For example, as discussed above, carbonnanotubes can be treated with acid to form carboxyl groups on the endsof the nanotubes, which can be further reacted to form acyl chlorides.The acyl chlorides can be reacted with, for example, amines such asRNH₂, where R═(CH₂)_(n)CH₃ and n=9-50, which can increase the solubilityof the nanotubes in organic solvents such as, for example, chloroform,dichloromethane, benzene, toluene, tetrahydrofuran, chlorobenzene andcombinations thereof. Additional description of solubilizing carbonnanotubes can be found in U.S. Pat. No. 6,331,262 to Haddon et al.,entitled “Method Of Solubilizing Shortened Single-Walled CarbonNanotubes In Organic Solutions,” which is hereby incorporated byreference herein.

Suitable polymers for use in the compositions of the present inventioninclude homopolmyers, copolymers, block copolymers and blends andcopolymers thereof. Suitable polymers include, for example,Polyetherimide (PEI), Polyimide (PI), Poly ether sulfone (PES), Polyphenyl sulfone (PPS), Poly sulfone, Polystyrene, Per fluoro alkoxy(PFA), Fluorinated Ethylene Propylene (FEP), ETFE, polybutyleneterephthalate (PBT), polyolefins (PO), polyethylene trerphthalate (PET),styrene block co-polymers (e.g. Kraton®), styrene-butadiene rubber,nylon in the form of polyether block polyamide (PEBA),polyetheretherketone (PEEK), poly(vinylidenefluoride),poly(tetrafluoroethylene) (PTFE), polyethylene, polypropylene,poly(vinylchloride) (PVC), ethyl vinyl acetate, and blends andcopolymers thereof. In general, the selection of a particular polymerfor use in the composition will be guided by the intended application ofthe composition. In some embodiments, the polymers can be functionalizedto contain functional groups suitable for reacting with the functionalgroups on the derivatized nanotubes to form composites where thenanotubes are covalently bonded to the polymers. Suitable functionalgroups include, for example, amines, alcohols, alkyl lithium compounds,hydrazines, and combinations thereof. Alternatively, the selectedpolymer can contain suitable functional groups such thatfunctionalization of the polymer is not required. For example,polyamides such as nylon can contain un-reacted amine groups which canreplace chloride groups on the functionalized nanotubes.

In general, the improved compositions comprise a polymer associated withcarbon nanotubes. In some embodiments, the composition is not soluablein water and in particular, the polymer may not be soluble in water.Generally, the carbon nanotubes are present in a concentration less thanabout 50 percent by weight. In some embodiments, the carbon nanotubesare present in a concentration from about 0.1 percent by weight to about40 percent by weight and in other embodiments the nanotubes can bepresent in a concentration form about 1 percent by weight to about 20percent by weight. One of ordinary skill in the art will recognize thatadditional ranges within these explicit ranges are contemplated and arewithin the scope of the present disclosure.

In embodiments where preserving the transparency of the polymer isdesired, the composition generally comprises carbon nanotubes at aconcentration of less than about 0.5 percent by weight. Additionally,single wall carbon nanotubes tend to preserve transparency better thanthe multiple wall carbon nanotubes. In embodiments where it is desiredto enhance the strength and/or thermal stability of the polymer, thecarbon nanotubes can be incorporated into the polymer at a concentrationfrom about 5 percent by weight to about 50 percent by weight.

Additionally, in some embodiments, the composition can further comprisesadditional components such as surfactants, fillers, processing aids,viscosity modifiers and the like. Generally, the additional componentsare each present at a concentration of no more than about 5 percent byweight. In particular, some embodiments of the present invention maycomprise liquid dispersions of carbon nanotubes in a solvent. In theseembodiments, the solvent can be removed during and/or after processingsuch that the final polymer/nanotube composite comprises less than 1percent by. weight of the solvent.

In some embodiments, the composition can comprise some or all of thecarbon nanotubes covalently bonded to the polymer. Specifically, thecomposites can comprise at least about 25 weight percent of the carbonnanotubes being covalently bonded to the polymer, in further embodimentsat least about 40 weight percent, in additional embodiments at leastabout 75 weight percent and in other embodiments at least about 95wieght percent of the carbon nanotubes are covalently bonded to thepolymer. A person of ordinary skill in the art will recognize thatadditional ranges of covalent bonding amounts within the explicit rangesare contemplated and are within the present disclosure. Reacting thecarbon nanotubes into a polymer can increase the dispersion of thenanotubes throughout the polymer and permits an atomic level order ofthe carbon nanotubes.

In general, the molecular weights of the polymers, the number offunctional groups on the polymers, the relative amounts of the nanotubesand the polymer and the like influence the chemical structure of thecomposites. Similarly, these features can be adjusted to obtain acomposite with desired properties. For example, the functionalizednanotubes can be used to cross link multifunctional polymers, such thatthe polymer chains are connected by the carbon nanotubes. In someembodiments, self-ordering composites can be formed with propertiesreminiscent of block copolymers can be formed.

The composite structures can be formed under processing conditions thatinvolve generally predictable bonding of the polymer with the nanotubes.For example, the polymers can have a single functional group for bondingwith the functionalized nanotubes. The molecular weights of the polymerscan be selected to yield appropriate structures in view of the sizes ofthe nanotubes. The processing conditions and the functionalization canbe controlled to generally form structures with a single polymer chainbonded with a single nanotube. By analogy with polymer block copolymers,this polymer-block-nanotube structure can exhibit standard blockcopolymer behavior with the nanotubes having the properties of one blockand the polymer having the properties of a second block. Similar,multiple block structures can be formed These blocked structures canexhibit self-ordering.

Composite Processing

The compositions of the present disclosure, which generally comprisecarbon nanotubes associated with a polymer, can be processed directlyinto desired articles by processes such as extrusion, injection moldingand the like and/or can be incorporated into a process to provide acoating or layer on a preformed article. In some embodiments, the carbonnanotube can be associated with the polymer by mechanically blending ormixing the nanotubes into a polymer. In other embodiments, the carbonnanotubes can be functionalized and reacted with a polymer to form apolymer/carbon nanotube composite structure. As described above,functionalizing the nanotubes can make the nanotubes more dispersable ina polymer, which can increase the uniformity of the nanotubes throughoutthe polymer. In some embodiments, the composites can be produced and thearticles formed in one continuous process, while in other embodimentsthe production of the composite and the formation of an article from thecomposite can be done separately.

In general, the bonding between a functionalized carbon nanotube and asuitable polymer can be performed in solution, in a polymer melt or somecombination thereof, such as the blending of a carbon nanotubedispersion and polymer melt. In general, the nanotubes are mixed throughthe polymer composition to form a roughly uniform composition. Asignificant amount of shear may be applied to combine the materials.

In some embodiments, to form a polymer/nanotube composite, a liquidnanotube dispersions can be formed and injected into an extruder havinga polymer within the extruder, wherein the extruder can provide shear toblend the carbon nanotubes within the polymer to obtain a compositehaving suitable mixing of the nanotubes throughout the polymer. Asdescribed further below, it may be desirable to include a hydorphylicpolymer, in particular ethyl vinyl acetate, to facilitate dispersion ofthe carbon nanotubes. In other embodiments, the nanotubes can beintroduced into an extruder in an agglomerated particle form by using asolid feeder or the like, and combined with a polymer located within theextruder to form a nanotube/polymer composite. In general, suitableextruders are available commercially. The extruder can be a single screwor multiple screw extruder, such as a two screw extruder. Suitablecommercial extruders include, for example, Berstorff model ZE or KEextruders (Hannover, Germany), Leistritz model ZSE or ESE extruders(Somerville, N.J.) and Davis-Standard mark series extruders (Pawcatuck,Conn.).

In general, dispersions can be formed with the carbon nanotubes inaqueous or non-aqueous dispersants. Processing aids can be used, such assurfacants and the like. In particular, the dispersion can comprise anaqueous dispersion of carbon nanotubes and ethyl vinyl acetate. It hasbeen discovered that ethyl vinyl acetate (EVA) can stabilize an aqueousdispersion of carbon nanotubes. In other embodiments, the dispersion cancomprise an aqueous dispersion of carbon nanotubes and a poly alcohol.Generally, any poly alcohol that is soluble or partially soluble inwater can be used to form the dispersions. In one embodiment, thedispersion can comprise an aqueous dispersion of carbon nanotubes inpoly(vinyl alcohol) (PVA). In some embodiments, the polymer/nanotubesdispersion can comprise a weight ratio of polymer to nanotubes fromabout 0.005 to about 1, while in other embodiments from about 0.01 toabout 0.67. One of ordinary skill in the art will recognize thatadditional ranges of concentration ratios of polymer to nanotubes withinthese explicit ranges are contemplated and are within the scope of thepresent disclosure. In some embodiments, to form the liquid nanotubedispersions, desired amounts of nanotubes and liquid along with anoptional polymer such as EVA and/or PVA, can be combined and mixed byany suitable processing apparatus such as a blender, mixer or the like.The liquid nanotube dispersion can then be injected into an extruder ora high shear mixer and mixed with a polymer material that is present inthe extruder/mixer. Generally, any liquids used to form thepolymer/nanotube dispersion can be evaporated during the extrusionprocess such that the final composite is substantially free of solvents,processing aids and other liquids. Vapors from the liquid can be ventedfrom the extruder as appropriate. In general, the polymer in theextruder can be introduced into the extruder by, for example, a hopperor other feeding apparatus, and the feeding apparatus can be heated tofacilitate the process by softening the polymer.

Generally, the extruder can apply shear forces to the nanotube polymermixture such that the nanotubes are mixed throughout the polymer to forma nanotube/polymer composite. In embodiments employing functionalizednanotubes, the shear forces applied by the extruder can promote reactionof the nanotubes with a suitable polymer(s) to form a compositestructure in which the nanotubers are covalently attached to thepolymer. Additionally, the nanotube/polymer composite can be directlyprocessed into articles having desired size and shape by processes suchas, for example, calandering, injection molding, compression molding andthe like. For example, the composite can be feed from the extruder to ainjection molding or compression molding apparatus such that theproduction of the nanotube/polymer composite and the formation of anarticle from the composite is a single process. In other embodiments,the extruder can be used to form an article by injecting the compositethrough a die and calandering the composite to form an article having adesired shape. One of ordinary skill in the art will recognize that theselection of a particular shaping process can be guided by the intendedapplication of a particular article. Alternatively, the composite formedin the extruder or other mixing apparatus can be collected in pellets orother desirable form and stored for subsequent processing into a finalarticle.

In one embodiment, the nanotube/polymer composite can be feed from theextruder to an injection molding apparatus where the composite can beformed into a bipolar plate suitable for use in electrochemical cellapplications. In these embodiments, the mold can be designed such thatthe bipolar plate has reactant flow channels formed into each side ofthe plate suitable for providing flow path for gasses. In otherembodiments, the polymer/nanotube composite can be feed from theextruder to a mold where the composite can be molded into a containersuitable for transporting semi-conductor wafers. In these embodiments,the mold can designed such that the container has structural elementssuitable for supporting the semi-conductor wafers.

In further embodiments, the carbon nanotubes/polymer composite can becoated onto an article by coating the article with a solvent/compositemixture or by forming the composite into a thin film that is laminatedor calendered onto the surface of the structure. For solution basedapproaches, once the solvent evaporates, the carbon nanotubes/polymercomposite can be deposited onto a surface of the article. In theseembodiments, any appropriate means for coating can be used to apply thesolvent/composite mixture to the article including, for examplespraying, dip coating or the like. Additionally, in these embodiments,the solvent/dispersant can be, for example, a suitable commerciallyavailable solvent that can disperse or suspend the carbonnanotubes/polymer composite. In some embodiments, the solvent may be anon-polar solvent such as, for example, 1,2-dichlorobenzene. Thesolubility of single wall carbon nanotubes is generally discussed in,for example, “Dissolution of Small Diameter Single-Wall Carbon NanotubesIn Organic Solvents?,” Bahr et al., Chem. Commun., pp. 193-194 (2001),which is hereby incorporated by reference herein. The polymer coatedcarbon nanotubes can then be used to coat an article such as, forexample, a wafer carrier to provide an electrically conductive coatingon the carrier.

Articles Formed From Composites

Articles, such as containers, carriers, fluid handling equipment,electrodes, electrically conductive elements for electrochemical cellsand the like, can be formed from the polymer/carbon nanotubecompositions described herein. Additionally or alternatively, an articlecan be coated with a polymer/carbon nanotube composition to form a layeron the surface of the article. In further embodiments, a coatingcomprising carbon nanotubes dissolved or suspended in a solvent can beapplied to an article to form a coating on the surface of the article.Articles formed by polymer/nanotube composites and/or articles having ananotube coating can have enhanced electrical and mechanical properties.Due to improved wear properties, some articles such as, containers, madefrom coating of polymer/nanotube composites can be refurbished and/orreused without a significant reduction of the mechanical and electricalproperties of the container over reasonable periods of time.

In some embodiments, the polymer/carbon nanotube composition can beformed into a container by injection molding, compression molding or thelike. In some embodiments, the containers can have structure on theinterior of the container suitable for holding a plurality of productsin a desired orientation within the container. For example, thecontainer can be designed to hold a plurality of semi-conductor devices,while in other embodiments the container may be design to hold siliconwafers. A container designed to hold silicon wafers is described in, forexample, U.S. Pat. No. 6,428,729 to Bhatt et al., entitled “CompositeSubstrate Carrier,” which is hereby incorporated by reference herein.Additionally, a tray for semiconductor devices is described inapplication Ser. No. 10/194,948, filed on Jul. 12, 2002, entitled “Trayfor Semiconductors,” which is hereby incorporated by reference herein.Due to the carbon nanotubes, the containers or appropriate surfacesthereof can be electrically conductive and can reduce the build up ofelectrostatic charges, which may reduce the occurrence of ESD damage tothe products contained within the container. In some embodiments, thewafer carrier or trays can comprise slots for supporting semi-conductorwafers, and the slots can comprise wafer contacts points having asurface with a composite of polymer associated with carbon nanotubes.The carbon nanotubes can be covalently attached to the polymer, blendedinto the polymer to form a physical composite, or a combination thereof.Since low levels of carbon nanotubes may be effective to generatedesired levels of electrical conductivity especially if applied as acoating, the containers made out of the compositions of the presentdisclosure can have the ability to reduce ESD without the transparencyof the container being compromised.

In other embodiments, a product such as a container can be formed from athermoplastic material, and subsequently coated with a coating layercomprising a polymer associated with carbon nanotubes. In someembodiments, the product can be composed of the same polymer used toform the coating layer, while in other embodiments the polymer used toform the product can be a different polymer than the polymer used toform the coating layer. In these embodiments, the product can be coatedwith the coating layer by any suitable means including, for example, dipcoating, spray coating, brushing, calendering, knife coating and/or thelike. In some embodiments, the coating layer can be from about 0.0005inches to about 0.005 inches thick, although a person of ordinary skillin the art will recognize that additional ranges within the explicitrange are contemplated and are within the present disclosure. In furtherembodiments, the polymer/carbon nanotube compositions can be used toform electrically conductive structures such as bipolar plates,electrodes, gas diffusion electrodes for fuel cells, current collectors,components thereof and the like. In general, bipolar plates of a fuelcell are electrically conductive structures that electrically connectthe anode of one electrochemical cell with the cathode of an adjacentelectrochemical cell. Additionally, in a hydrogen/oxygen fuel cell, thebipolar plates generally have channels that provide flow pathways foroxygen to reach the cathode and hydrogen to reach the anode. Forexample, a bipolar plate can have horizontal channels on one side of theplate and vertical channels on the other side of the plate. The platescan be formed, for example, by injection molding or compression molding.In addition to providing electrical conductivity, the bipolar platesformed from compositions comprising carbon nanotubes can have greatermechanical strength, resistance to chemical degradation and thermalstability compared with bipolar plates formed from other materials.Bipolar plates suitable for use in electrochemical cell applications aredisclosed, for example, in U.S. Pat. No. 6,677,071 to Yang, entitled“Bipolar Plate For A Fuel Cell,” and U.S. Pat. No. 6,503,653 to Rock,entitled “Stamped Bipolar Plate For PEM Fuel Cell Stack,” which arehereby incorporated by reference herein.

The polymer/nanotube compositions of the present disclosure can also beused to form electrode structures suitable for use in electrochemicalcell applications. Generally, electrodes can comprise an active layerassociated with a backing layer. The backing layer can be impervious toelectrolyte but preamble to gas, while the active layer can be a porousstructure comprising catalyst particles suitable for catalyzing theelectrochemical reactions, conductive particles and a porous particlebinder. In some embodiments, the polymer/nanotube composite can beprocessed, along with suitable catalytic particles, to form a porousactive layer, which can be attached to a backing layer by adhesives orlamination to form an electrode structure. Suitable catalyst particlesinclude, for example, platinum powders.

Generally, products, such as containers, made from a polymer/carbonnanotube composition, or products coated with a polymer/carbon nanotubecomposition, can be reused repeatedly, i.e., recycled without losing theelectrically conductive properties. Thus, products made from thecompositions of the present disclosure can be recycled and formed intorecycled products, which retain the electrical products of the originalproduct through many uses. Thus, the products may be less expensive touse relative to products that can only be used one or a few timeswithout reapplying the electrically conductive coating.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. Although the presentinvention has been described with reference to particular embodiments,workers skilled in the art will recognize that changes may be made inform and detail without departing from the spirit and scope of theinvention.

1. A composition comprising a polymer covalently bonded to the sidewalls of carbon nanotubes.
 2. The composition of claim 1 wherein thenanotubes comprise single wall carbon nanotubes, multiple wall carbonnanotubes, or a combination thereof.
 3. The composition of claim 1wherein the carbon nanotubes are present in a concentration of less thanabout 50 percent by weight.
 4. The composition of claim 1 wherein thecarbon nanotubes are present in a concentration from about 0.1 percentby weight to about 40 percent by weight.
 5. The composition of claim 1wherein the polymer is selected from the group consisting of PEI,Polyimide, Poly ether sulfone (PES), Poly phenyl sulfone (PPS), Perfluoro alkoxy (PFA), Fluorinated ethylene propylene (FEP), Ethylene trifluoro ethylene (ETFE) Poly sulfone, Polystyrene, Poly ether Ketone(PEK), Poly ether ketone ketone (PEKK), polybutylene terephthalate(PBT), polyolefins (PO), polyethylene terephthalate (PET), styrene blockco-polymers, styrene-butadiene rubber, nylon in the form of polyetherblock polyamide (PEBA), polyetheretherketone (PEEK),poly(vinylidenefluroide), poly(tetraflurorethylene) (PTFE),polyethylene, polypropylene, poly(vinylchloride) (PVC), ethyl vinylacetate and blends and copolymers thereof.
 6. The composition of claim 1wherein the carbon nanotubes have functional groups attached to the sidewalls that bridge between the walls of the nanotubes and the polymer. 7.The composition of claim 6 wherein the polymer is a multifunctionalpolymer having two or more functional groups that are covalently bondedwith carbon nanotubes.
 8. The composition of claim 7 wherein the polymeris covalently bonded to the nanotubes to form polymer-nanotubestructures that can self order.
 9. The composition of claim 7 whereinthe polymer is covalently bonded to the nanotubes such that polymerchains are crosslinked by the nanotubes.
 10. An article comprising thecomposition of claim
 1. 11. The article of claim 10 wherein the articlecomprises a wafer carrier suitable for transporting semi-conductorwafers.
 12. The article of claim 10 wherein the article comprises abipolar plate.
 13. The article of claim 10 wherein the article comprisesan electrode.
 14. A liquid dispersion comprising ethyl vinyl acetate andcarbon fibers.
 15. The liquid dispersion of claim 14 wherein the carbonfibers comprise single wall carbon nanotubes, multiple wall carbonnanotubes or a combination thereof.
 16. The liquid dispersion of claim14 wherein the carbon fibers are present in a concentration of less thanabout 50 percent by weight.
 17. The liquid dispersion of claim 14wherein the carbon fibers are presenting a concentration from about 0.1percent by weight to about 40 percent by weight.
 18. The liquiddispersion of claim 14 wherein the carbon fibers comprise functionalgroups located on the ends of the nanotubes, along the side walls of thenanotubes, or both.
 19. The liquid dispersion of claim 18 wherein thefunctional groups comprise fluorine.
 20. The liquid dispersion of claim14 wherein the dispersion comprises an aqueous dispersion.
 21. Theliquid dispersion of claim 14 wherein the EVA has a melt index fromabout 2 g/10 mn to about 800 g/10 mn as determined by ASTM D1238procedure with a temperature of 190° C. and a load of 2.16 Kg.
 22. Theliquid dispersion of claim 14 wherein the EVA has a density from about0.92 g/cm³ to about 0.95 g/cm³.
 23. The liquid dispersion of claim 14wherein the EVA has a VA content from about 20 percent to about 30percent.
 24. The liquid dispersion of claim 14 wherein the weight ratioof EVA to nanotubes is from about 0.005 to about
 1. 25. A liquiddispersion comprising poly(vinyl alcohol) and carbon fibers.
 26. Anarticle comprising a polymer and fluorinated carbon nanotubes.
 27. Thearticle of claim 25 wherein the carbon nanotubes comprise single wallcarbon nanotubes, multiple wall carbon nanotubes or a combinationthereof.
 28. The article of claim 26 wherein the fluorinated carbonnanotubes are covalently bonded to the polymer.
 29. The article of claim26 wherein the fluorinated carbon nanotubes a mixed throughout thepolymer.
 30. The article of claim 26 wherein the polymer and fluorinatedcarbon nanotubes are coated onto the surface of the article.
 31. Thearticle of claim 26 wherein the fluorinated carbon nanotubes are presentin a concentration of less than about 50 percent by weight.
 32. Thearticle of claim 26 wherein the fluorinated carbon nanotubes are presentin a concentration from about 0.1 percent by weight to about 40 percentby weight.
 33. The article of claim 26 wherein the polymer is selectedfrom the group consisting of polybutylene terephthalate (PBT),polyolefins (PO), polyethylene terephthalate (PET), styrene blockco-polymers, styrene-butadiene rubber, nylon in the form of polyetherblock polyamide (PEBA), polyetheretherketone (PEEK),poly(vinylidenefluroide), poly(tetraflurorethylene) (PTFE),polyethylene, polypropylene, poly(vinylchloride) (PVC), ethyl vinylacetate and blends and copolymers thereof.
 34. The article of claim 26wherein the article comprises a wafer carrier having structural elementssuitable for transporting a plurality of semi-conductor wafers.
 35. Thearticle of claim 26 wherein the article comprises a bipolar platesuitable for use in electrochemical cells.
 36. A method of forming acomposite, the method comprising injecting a liquid dispersion of carbonfibers within an extruder having a polymer within the extruder andapplying shear to blend the carbon fibers and the polymer.
 37. Themethod of claim 36 wherein the liquid dispersion of carbon fiberscomprises an aqueous dispersion of carbon fibers and ethyl vinylacetate.
 38. The method of claim 37 wherein the carbon fibers comprisesingle wall carbon nanotubes, multiple wall carbon nanotubes, or acombination thereof.
 39. The method of claim 37 wherein the carbonfibers are present at a concentration of less than about 50 percent byweight.
 40. The method of claim 37 wherein the carbon fibers are presentat a concentration from about 0.1 percent by weight to about 40 percentby weight.
 41. The method of claim 36 wherein the carbon fibers comprisefunctional groups that can covalently bond with the polymer, whereincovalent bonding between the carbon fibers and the polymer occurs in theextruder.
 42. The method of claim 36 wherein the composite is fed fromthe extruder to a shaping apparatus where the composite is formed intoan article having a desired shape and size.
 43. The method of claim 42wherein the shaping apparatus is selected form the group consisting ofrollers, injection molds, compression molds, and combinations thereof.44. The method of claim 36 wherein the composite is feed from theextruder and coated onto an article to provide a layer of the compositeon a surface of the article.
 45. The method of claim 36 wherein theextruder comprises a twin-screw extruder.
 46. A wafer carrier comprisinga slot for the support of a wafer, wherein the slot comprises wafercontact points having a surface with a composite of polymer associatedwith carbon nanotubes.
 47. The wafer carrier of claim 46 wherein carbonnanotubes are mixed throughout the polymer.
 48. The wafer carrier ofclaim 46 wherein the carbon nanotubes are covalently bonded to thepolymer.
 49. The wafer carrier of claim 46 wherein the carbon nanotubescomprise single wall carbon nanotubes.
 50. The wafer carrier of claim 46wherein the carbon nanotubes are present in a concentration of less thanabout 1 percent by weight.
 51. The wafer carrier of claim 46 wherein thecarbon nanotubes are present in a concentration less than about 0.5percent by weight.
 52. The wafer carrier of claim 46 wherein thetransparency of the polymer not affected by the carbon nanotubes. 53.The wafer carrier of claim 46 wherein the composite reduceselectrostatic discharge relative to carriers made of plastic.
 54. Thewafer carrier of claim 46 wherein the polymer is selected from the groupconsisting of polybutylene terephthalate (PBT), polyolefins (PO),polyethylene terephthalate (PET), styrene block co-polymers,styrene-butadiene rubber, nylon in the form of polyether block polyamide(PEBA), polyetheretherketone (PEEK), poly(vinylidenefluroide),poly(tetraflurorethylene) (PTFE), polyethylene, polypropylene,poly(vinylchloride) (PVC), ethyl vinyl acetate and blends and copolymersthereof.
 55. A fuel cell comprising a bipolar plate, the bipolar platecomprising a composite of polymer associated with carbon nanotubes. 56.The bipolar plate of claim 55 wherein the carbon nanotubes are mixedwithin the polymer.
 57. The bipolar plate of claim 55 wherein the carbonnanotubes are covalently bonded to the polymer.
 58. The bipolar plate ofclaim 55 wherein the carbon nanotubes comprise single wall carbonnanotubes, multiple wall carbon nanotubes, or a combination thereof. 59.The bipolar plate of claim 55 wherein the carbon nanotubes are presentin a concentration from about 1 percent by weight to about 50 percent byweight.
 60. The bipolar plate of claim 55 wherein the polymer isselected from the group consisting of polybutylene terephthalate (PBT),polyolefins (PO), polyethylene terephthalate (PET), styrene blockco-polymers, styrene-butadiene rubber, nylon in the form of polyetherblock polyamide (PEBA), polyetheretherketone (PEEK),poly(vinylidenefluroide), poly(tetraflurorethylene) (PTFE),polyethylene, polypropylene, poly(vinylchloride) (PVC), ethyl vinylacetate and blends and copolymers thereof.
 61. The bipolar plate ofclaim 55 further comprising a first side and a second side wherein thefirst side comprises reactant flow channels formed into the surface ofthe plate.
 62. The bipolar plate of claim 61 wherein the second sidecomprises reactant flow channels formed into the surface of the plate.